With presently known electronic phase shifting circuits phase changes of up to one cycle or 360 degrees are accomplished by varying a control voltage between a lower limit and an upper limit. The lower limit may correspond to zero degrees whereas the upper limit may correspond to an angle slightly in excess of 360 degrees to assure that all angles between zero and 360 degrees are attainable. In as much as phases of more than 360 degrees have corresponding values less than 360 degrees, it is not necessary nor practical to design any circuit wherein the upper voltage limit of which would permit phase changes significantly greater than 360 degrees. Thus if it were desired to shift phase from, say, 360 degrees to 440 degrees, the control voltage would be lowered from near its upper limit at 360 degrees down to a lower value corresponding to 80 degrees (the equivalent of 440 degrees). During this change or "flyback" in voltage, passage occurs through all phase angles between 360 and 80 degrees. In many phase shifter applications the transition time for such "flybacks" is relatively long and undesirable.
For example, if the phase shifter is employed to steer a radar antenna beam to a particular target location, passage of the beam through other angles will reduce the response time of the system in arriving at the target's azimuth. It is therefore desirable to have a phase shift that responds essentially instantaneously to a new command position.
In other applications such as, for example, closed-loop feed-back systems, if the time necessary to detect an error condition is less than the time required for the phase to "flyback" to the corrected value, undesirable or detrimental instabilities or oscillations may occur which further serve to impede the correction process. By way of example, assume an error signal calling for a phase correction from 360 degrees to 440 degrees. Since the control voltage is near its upper limit at 360 degrees and can go no higher toward 440, such voltage must be reduced to a lower value which will correspond to a phase of 80 degrees. If the time for such reduction is longer than the time constant of the phase error detection, then an even greater error will be detected as the phase passes below its initial value of 360 degrees on its way to the corrected value of 80 degrees. At the same time a new correction signal will be generated attempting to increase the control voltage and cause the phase to change direction away from the desired angle, thereby creating unnecessary delay before stabilization at the corrected angle. It is therefore desirable to have the correction in phase take place substantially instantaneously or within the time constant of the error detection function.